Etymology

The term Greater Toronto has been used in writing as early as the 1900s, although at the time, the term only referred to the former City of Toronto and its immediate townships and villages, which became Metropolitan Toronto in 1954 and became the current city of Toronto in 1998. The usage of the term involving the four regional municipalities came into formal use in the mid-1980s, after it was used in a widely discussed report on municipal governance restructuring in the region and was later made official as a provincial planning area. However it did not come into everyday usage until the mid- to late 1990s. In 2006, the term began to be supplanted in the field of spatial planning as provincial policy increasingly began to refer to either the "Greater Toronto and Hamilton Area" (GTHA) or the still-broader "Greater Golden Horseshoe". The latter includes communities like Barrie, Guelph and the Niagara Region. The GTA continues, however, to be in official use elsewhere in the Government of Ontario, such as the Ministry of Finance.

Census metropolitan area A map of Toronto's Census Metropolitan Area, which contains a large portion of the Greater Toronto Area.

Some municipalities that are considered part of the GTA are not within Toronto's Census Metropolitan Area (CMA) whose land area (5,904 km² in 2006) and population (5,583,064 as of the 2011 census) is thus smaller than the land area and population of the GTA planning area. For example, Oshawa, which is the centre of its own CMA, or Burlington, which is included in the Hamilton CMA are both deemed part of the Greater Toronto Area. Other municipalities, such as New Tecumseth in southern Simcoe County and Mono Township in Dufferin County are included in the Toronto CMA but not in the GTA. These different border configurations result in the GTA's population being higher than the Toronto CMA by nearly one-half million people, often leading to confusion amongst people when trying to sort out the urban population of Toronto.

Other nearby urban areas, such as Hamilton, Barrie or St. Catharines-Niagara and Kitchener-Waterloo, are not part of the GTA or the Toronto CMA, but form their own CMAs that are in fairly close proximity to the GTA. Ultimately, all the aforementioned places are part of the Golden Horseshoe metropolitan region, an urban agglomeration, which is the fifth most populous in North America. When the Hamilton, Oshawa and Toronto CMAs are agglomerated with Brock and Scugog, they have a population of 6,170,072. It is part of the Great Lakes Megalopolis, containing an estimated 54 million people.

Extended area Main article: Greater Toronto and Hamilton Area

The term "Greater Toronto and Hamilton Area" (GTHA) refers to the usual GTA plus the former Regional Municipality of Hamilton–Wentworth, which was amalgamated to become the City of Hamilton in 2001.